Influence of Silver Doping on Photocatalytic Activity of Liquid-Flame-Sprayed-Nanostructured TiO2 Coating

Silver ion was added to liquid feedstock to deposit Ag⁺-doped-nanostructured TiO₂ photocatalytic coatings through liquid-flame spraying. The coating microstructure was characterized by x-ray diffraction (XRD). The photocatalytic performance of coatings was examined by photodegradation of acetaldehyde. The XRD analysis showed that the phase structure of coatings was not significantly influenced by the silver ion doping. However, a shift was found for XRD peaks of anatase TiO₂. The photocatalytic activity of the TiO₂ coatings increased and then decreased with the increase of dopant concentration. The photocatalytic activity of doped coatings was higher than that of pure TiO₂ coating, regardless of the dopant concentration. The enhancement of photocatalytic performance of doped coatings is attributed to co-doping of Ag⁺ ion and metallic Ag. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

热喷涂法制备的La3+掺杂纳米TiO2粉末的表征

采用等离子热喷涂法以钛酸四丁酯为主要原料制备出稀土离子掺杂的纳米TiO2光催化剂.通过XRD,XPS,TEM,UV-Vis等检测手段对样品进行表征,同时检测了其光催化性能,并分析了掺杂对TiO2的影响机理.结果表明,所制备的La3 掺杂纳米TiO2是锐钛矿相和金红石相混晶结构,粒径分布在10～50nm之间;La3 掺杂能够促进锐钛矿向金红石的转变,同时抑制TiO2晶粒的长大;La3 掺杂使TiO2紫外-可见吸收光谱发生红移;适量La3 掺杂能显著提高TiO2的光催化活性,最佳掺杂浓度为0.5%(与Ti原子摩尔比),甲基橙降解率在90min内可达到82.4%.比纯TiO2高出13.2%.     

Characterization of microstructure of Nano-TiO2 coating deposited by vacuum cold spraying

Control of the microstructure of TiO₂ coatings through preparation methods significantly influences the coating performance. In this study, a vacuum cold-spray process, as a new coating technology, is used to deposit nanocrystalline TiO₂ coatings on conducting glass and stainless steel substrates. TiO₂ deposits were formed using two types of nanocrystalline TiO₂ powders with mean particle diameters of 200 and 25 nm. Coating microstructures were characterized by scanning electron microscopy and x-ray diffraction analysis. Results demonstrate that a thick nanocrystalline TiO₂ coating can be deposited by the vacuum cold-spray process. The coating was found to consist of particles stacked as agglomerates that build up to several hundred nanometers. The coating also presents a mesoporous microstructure that could be effective in such applications as photocatalytic degradation and dye-sensitized solar cells. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Characteristics of N-doped TiO2 nanotube arrays by N2-plasma for visible light-driven photocatalysis

N-doped TiO₂ nanotube arrays were prepared by electrochemical anode oxidation of Ti foil followed by treatment with N₂-plasma and subsequent annealed under Ar atmosphere. The morphologies, composition and optical properties of N-doped TiO₂ nanotube arrays were characterized using field-emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectrometer (XRD), Photoluminescence (PL) and UV-vis diffusion reflection spectroscopy (UV-vis DRS). Methylene blue (MB) solution was utilized as the degradation model to evaluate the photocatalytic activity of the samples under visible light irradiation. The results suggested N₂-plasma treatment created doping of nitrogen onto the surface of photoelectrodes successfully and the N-doped TiO₂ nanotube arrays display a significantly enhancement of the photocatalytic activity comparing with the pure TiO₂ nanotube arrays under the visible light irradiation.     

钽表面铜掺杂Ta2O5纳米棒的制备及抗菌性能研究

本实验采用两步水热法在钽基体表面制备出掺杂Cu_²⁺的Ta₂O₅纳米棒薄膜。采用XRD、SEM、XPS等方法分析了材料的物相和表面微观结构。用ICP检测了样品在生理盐水中离子析出浓度,最后通过平板计数法检验了不同含量铜掺杂Ta₂O₅薄膜的抗菌能力。结果表明,通过两步水热处理,在钽表面生成了简单斜方晶体结构的Ta₂O₅纳米棒阵列,Cu_²⁺的掺杂不会对纳米棒薄膜的微观形貌和物相造成显著影响。随时间的增加,掺铜薄膜的铜离子析出速率逐渐趋于平缓。平板计数法表明,Cu_²⁺ 的掺杂量达到2.68At%时,铜掺杂Ta₂O₅纳米棒薄膜的抗菌性能最好,抗菌率达99.2%。     

Characterization of TiO2 coatings prepared by a modified electric arc-physical vapour deposition system

TiO₂ thin coatings were prepared, on various substrates, through evaporation of metallic titanium in an oxidizing atmosphere by modified electric arc-physical vapor deposition (EA-PVD). The coatings were characterized chemically (by means of XPS and SIMS) and from the structural point of view (by means of XRD and Raman spectroscopy), in order to understand the factors which lead to homogeneous coatings with high anatase content. The type of substrate is the main parameter that influences the crystal structure of the coatings: when stainless steel is used as substrate the coatings consist essentially of rutile, while on glass substrates coatings containing mainly anatase are obtained. The photocatalytic activity of the samples upon UVA irradiation was tested by using phenol as the target molecule. Phenol in the solution can be photocatalytically and rapidly degraded through the EA-PVD anatase TiO₂ coatings.     

Comparison of the photocatalytic behavior of TiO2 coatings elaborated by different thermal spraying processes

This paper proposes a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying, and high-velocity oxyfuel spraying). Agglomerated spray dried anatase TiO₂ powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were studied mainly by scanning electron microscopy and x-ray diffraction. The photocatalytic behavior of the TiO₂-base surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure depended strongly on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying has allowed retention of the original anatase phase and for very reactive TiO₂ surfaces to be obtained for the removal of nitrogen oxides. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.     

Microstructural Analysis and Photocatalytic Activity of Plasma-Sprayed Titania-Hydroxyapatite Coatings

Hydroxyapatite (HAp Ca₁₀(PO₄)₆(OH)₂) is known to be a biomaterial and an adsorbent for chromatography. In this study, HAp was agglomerated with anatase TiO₂ to manufacture thermal-spray powders to improve the adsorption activity of TiO₂, and then to improve its photocatalytic activity. The microstructures, compositions and photocatalytic activity of plasma-sprayed TiO₂, TiO₂-10%HAp, TiO₂-30%HAp, and HAp coatings were investigated. Due to the low thermal conductivity of HAp compound, not all HAp particles fully melted even under the arc current of 800 A. The addition of HAp inhibited the phase transformation of anatase TiO₂ to rutile. Under the arc current of 600 A, the anatase content in the TiO₂, TiO₂-10%HAp and TiO₂-30%HAp coatings was 11, 20 and 42%, respectively. With the increasing of the spraying distance from 70 to 110 mm, the anatase content in the TiO₂-30%HAp coatings decreased from 34 to 17% under arc current of 700 A. Furthermore, a slight decomposition of HAp to α-Ca₃(PO₄)₂ was found in the TiO₂-30%HAp coatings, it did not decompose to CaO and P₂O₅ according to the XRD and EDAX analysis. The addition of the secondary gas of helium had no significant influence on the melting state of the TiO₂-HAp feedstock powders. Moreover, the HAp in the TiO₂-10%HAp and TiO₂-30%HAp coatings had adsorption characteristic to acetaldehyde. The photocatalytic activity of TiO₂-10%HAp coating was highest among TiO₂, TiO₂-10%HAp, and TiO₂-30%HAp coatings sprayed under the arc current of 600 A for the optimum adsorption property and anatase content. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Effect of Nd2O3 addition on the surface phase of TiO2 and photocatalytic activity studied by UV Raman spectroscopy

TiO₂ modified with Nd₂O₃ (Nd-TiO₂) nanoparticles were prepared by a co-precipitation method and utilized as the photocatalysts for the degradation of Rhodamine B (RhB). The influence of Nd₂O₃ on the bulk and surface phase, surface area, particle size, and optical response of TiO₂ was investigated by X-ray diffraction (XRD), UV Raman spectroscopy, transmission electron microscopy (TEM), BET, and UV-visible diffuse reflectance spectra. It is found that the crystalline phase and phase composition in the bulk and surface region of Nd-TiO₂ calcined at high temperatures can be tuned by changing the amount of Nd₂O₃. Based on the results from XPS, EDX, XRD, and UV Raman spectra, it is assumed that Nd³⁺ ions do not enter the TiO₂ lattice, but highly disperse onto the Nd-TiO₂ particle surface in the form of Nd₂O₃ crystallites. These crystallites inhibit the agglomeration, growth in crystal size, and anatase-to-rutile phase transformation of TiO₂. In the photocatalytic degradation of RhB reaction, Nd-TiO₂ nanoparticles with higher surface area and wider optical response are more reactive in case of the same surface anatase phase. When the mixed phases of anatase and rutile exist in the surface region of Nd-TiO₂, the synergetic effect over surface area and optical response is the important parameter which determines optimal photocatalytic activity.     

液料等离子热喷法制备Fe3+/TiO2纳米粉末

通过对液料等离子热喷前驱物添加掺杂成分实现了液料等离子热喷TiO2纳米粉末的掺杂改性,并利用TEM,XRD及XPS对其进行表征.结果表明,采用液料等离子热喷法可以制备Fe3 掺杂TiO2纳米粉末,所制备粉末形貌基本呈球形或近球形,粒径分布为10～35 nm,掺杂量小于2.0%时粉末为锐钛矿及金红石相混晶,Fd3 掺杂促进锐钛矿向金红石相的转变,掺杂量为10.0%时析出了Fe2Ti3O9相.Fe3 掺杂不会引起TiO2粒径的大范围波动.粉末中含有O,Ti,Fe和C等元素,Fe元素在TiO2中仍为 3价.     

The effect of milling atmospheres on photocatalytic property of Fe-doped TiO2 synthesized by mechanical alloying

The Fe-doped TiO₂ powders were, respectively, milled in argon, air and oxygen atmospheres, the oxygen partial pressure (P_O2) of which increase in turn. The Fe concentration was found to be 4.468, 4.227 and 4.473 at.% for the powders milled in argon, air and oxygen, respectively. The rietveld refined of X-ray diffraction (XRD) revealed that the milled samples were pure rutile structure. The Raman spectra confirmed the results of XRD. Furthermore, it indicated that the amount of oxygen vacancies increased with the decrease of P_O2. Fe dissolved in TiO₂ was found to take Fe²⁺/Fe³⁺ ionic valences. The absorption edge was shifted to visible light range by the doping of Fe. And visible light photocatalytic activity enhanced with the decrease of P_O2 due to the increase of oxygen vacancies.     

Micro-arc oxidation of TC4 substrates to fabricate TiO2/YAG:Ce compound films with enhanced photocatalytic activity

This paper introduces a process for “in situ” preparing TiO₂ photocatalytic film compounded with YAG:Ce³⁺ semiconductor upon titanium alloy by using micro-arc oxidation (MAO). The surface morphology, chemical compositions, phase structures and photocatalytic properties of the films were characterized and measured by field emission gun scanning electron microscope (FEG-SEM), energy-dispersive X-ray spectrometer (EDS), X-ray diffractometer (XRD), electro-chemical workstation and UV-vis spectrophotometer. The results show that the YAG:Ce³⁺ semiconductor particles which were added in the electrolyte had been homogenously compounded within the TiO₂ film during MAO. Compared with the pure TiO₂ film, the compounded film exhibited much larger specific surface area, stronger absorption in the visible light and higher photo-generated current density, which improves the photocatalytic property markedly. It is expected that MAO will provide a simple, economic and promising approach for preparing a superior photocatalytic TiO₂ film.     

Photocatalytic activities of N doped TiO2 coatings on 316L stainless steel by plasma surface alloying technique

Nitrogen doped titanium dioxide (N-TiO₂) coatings were fabricated by oxidation of the TiN_x coatings in air. TiN_x coatings were prepared on stainless steel (SS) substrates by plasma surface alloying technique. The reference TiO₂ sample was also deposited by oxidation of the Ti coatings in air. The as-prepared coatings were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and ultra violet-visible absorption spectroscopy (UV-Vis). The formation of anatase type TiO₂ is confirmed by XRD. SEM measurement indicates a rough surface morphology with sharp, protruding modules after annealing treatment. The band gap of the N-doped sample is reduced from 3.25 eV to 3.08 eV compared with the undoped one. All the N-doped samples show red shift in photoresponse towards visible region and improved photocurrent density under visible irradiance is observed for the N-doped samples. The photocatalytic activity was evaluated via the photocatalytic oxidation of methylene blue (MB) in aqueous under visible light irradiation. The results reveal that the N-doped samples extend the light absorption spectrum toward the visible region. The degradation rate of N-TiO₂ is 20% in visible irradiation for 150 min.     

The induced synthesis of mixed phase niobate by Cu doping and its photocatalytic property

Cu-doped KNb₃O₈ photocatalysts were prepared using a simple solid-state method. The catalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectrum. XRD and SEM analyses suggest that Cu doping can induce the formation of the compound K₆Nb_10.8O₃₀ with tungsten-bronze structure and the relative content of K₆Nb_10.8O₃₀ in the Cu-doped samples increased with increasing Cu doping amount. When the Cu doping amount reaches 2 wt.%, the as-prepared sample is mainly composed of K₆Nb_10.8O₃₀. The photocatalytic properties of the catalysts were evaluated using the degradation of acid red G. The results showed that Cu-doping significantly increased the photocatalytic activity of the KNb₃O₈ catalyst. The optimum dopant concentration range of Cu was found to be 0.3-1 wt.%. The synergistic effect of Cu doping and mixed phase niobate compounds is responsible for the enhanced photocatalytic activity.     

Purifying behavior of photocatalytic TiO2 anodized in nitrate ion containing solution

Mesoporous titanium dioxide films were fabricated on titanium plates by micro-arc oxidation method. To increase the photocatalytic activity of the films, NH₄NO₃ was added to the H₂SO₄ solution, and anodizing was carried out at high voltages using a DC power supply. The crystal structure, chemical composition, surface morphology and the optical property of the films were investigated by XPS, XRD, UV-VIS spectroscopy and SEM. The photocatalytic activity of the films was evaluated by the decomposition of aniline blue, and the activity of the films for the degradation turned out to be improved by the additives to the electrolyte solution. The enhanced photocatalytic activity might result from the increased porosity and nitrate ion incorporation into the anodic films by micro arcing, and thereby the TiO₂ layer might exhibit an improved absorption property for the visible light.     

无模板剂的溶胶-水热法合成具有可见光响应的氮掺杂混晶 TiO2(锐钛矿/金红石/板钛矿)纳米棒束

采用无模板剂的溶胶-水热法制备了具有可见光响应的N掺杂锐钛矿/金红石/板钛矿型TiO_2(N-TiO_2)纳米棒束,并利用X射线衍射(XRD)、透射电镜(TEM)、紫外-可见光漫反射光谱(UV-Vis DRS)、傅里叶变换红外光谱(FTIR)和X射线光电子能谱(XPS)等手段对获得的样品进行了表征。以甲基橙为模型反应物,评价了N-TiO_2纳米棒束的光催化活性。表征结果结合光催化活性评价结果显示,与P25-TiO_2相比,N掺杂、混晶及纳米棒束之间的协同作用是所制备的混晶N-TiO_2纳米棒束具有良好光催化活性的主要原因,并对混晶N-TiO_2纳米棒束光催化降解甲基橙的机理进行了探讨。     

Fe掺杂TiO2纳米材料的合成及光催化性能

以钛酸丁酯为钛源,Fe(NO3)3·9H2O为铁源,采用溶胶-凝胶法制备Fe/TiO2纳米粉体,利用溶胶结合静电纺丝技术制备Fe/TiO2纳米纤维,从材料改性及形貌改善两个角度共同提高TiO2纳米材料的光催化活性及实用性。借助XRD、SEM、TEM等分析技术,探究了Fe/TiO2纳米材料在可见光区的光催化活性,分析了煅烧温度及掺铁量对Fe/TiO2纳米材料光催化性能的影响。结果显示,铁的掺入及形貌的改善有助于提高TiO2的光催化性能。     

Photocatalytic performance of nano-photocatalyst from TiO2 and Fe2O3 by mechanochemical synthesis

Nano-particles of homogeneous solid solution between TiO₂ and Fe₂O₃ (up to 10 mol%) have been prepared by mechanochemical milling of TiO₂ and yellow Fe₂O₃/red Fe₂O₃/precipitated Fe (OH)₃ using a planetary ball mill. Such novel solid solution cannot be prepared by conventional co-precipitation technique. A preliminary investigation of photocatalytic activity of mixed oxide (TiO₂/Fe₂O₃) on photo-oxidation of different organic dyes like Rhodamine B (RB), Methyl orange (MO), Thymol blue (TB) and Bromocresol green (BG) under visible light (300-W Xe lamp; λ > 420 nm) showed that TiO₂ having 5 mol% of Fe₂O₃ (YFT1) is 3-5 times higher photoactive than that of P25 TiO₂. The XRD result did not show the peaks assigned to the Fe components (for example Fe₂O₃, Fe₃O₄, FeO₃, and Fe metal) on the external surface of the anatase structure in the Fe₂O₃/TiO₂ attained through mechanochemical treatment. This meant that Fe components were well incorporated into the TiO₂ anatase structure. The average crystallite size and particle size of YFT1 were found to be 12 nm and 30 ± 5 nm respectively measured from XRD and TEM conforming to nanodimensions. Together with the Fe component, they absorbed wavelength of above 387 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the Fe₂O₃/TiO₂ particle attained through mechanochemical method. This meant that Fe components were well inserted into the framework of the TiO₂ anatase structure. EPR and magnetic susceptibility show that Fe³⁺ is in low spin state corresponding to μ_B = 1.8 BM. The temperature variation of μ_B shows that Fe³⁺ is well separated from each other and does not have any antiferromagnetic or ferromagnetic interaction. The evidence of Fe³⁺ in TiO₂/Fe₂O₃ alloy is also proved by a new method that is redox titration which is again support by the XPS spectrum.     

Synthesis and photoactivity of the highly efficient Ag species/TiO2 nanoflakes photocatalysts

Ag species/TiO₂ nanoflakes photocatalysts with different relative contents (Ag⁺, Ag²⁺, Ag⁰) have been successfully synthesized by a simple template-free synthetic strategy. X-ray photoelectron spectroscopy, X-ray diffraction, and UV-vis diffuse reflectance spectra indicated that the dopant ions (Ag⁺ or Ag²⁺) were partly incorporated into the titanium dioxide nanoflakes. Meanwhile, part of the silver ions migrated to the surface after the subsequent calcination and aggregated into ultra-small metallic Ag nanoclusters (NCs) (1-2 nm), which are well dispersed on the surface of TiO₂ nanoflakes. The photocatalytic activities of the Ag species/TiO₂ materials obtained were evaluated by testing the photodegradation of the azo dye reactive brilliant X-3B (X-3B) under near UV irradiation. Interestingly, it was found that the maximum photocatalytic efficiency was observed when Ag species coexisted in three valence states (Ag⁺, Ag²⁺, Ag⁰ NCs), which was higher than that of Degussa P25. The high photocatalytic activity of the Ag species/TiO₂ can be attributed to the synergy effect of the three Ag species.     

TiO2/膨润土复合光催化材料的常温制备及性能研究

采用改进的溶胶-凝胶法,在以水为主要溶剂的反应体系中,控制钛酸四丁酯充分水解、缓慢聚合,在 常压、低温(70℃)的温和条件下制备出稳定的TiO₂纳米晶溶胶,并利用TiO₂纳米晶溶胶在膨润土表面负载,获得TiO₂/膨润土复合光催化材料。采用 X 射线衍射、扫描电镜、比表面积测定等研究手段对样品的结构形貌进行了表征,并考察了其光催化活性。结果表明：较高的水用量有利于TiO₂晶体形成,当去离子水:钛酸四丁酯摩尔比大于167:1时,在溶胶体系中出现了锐钛矿型TiO₂纳米晶体;TiO₂纳米晶主要负载于膨润土表面,并未嵌入到膨润土层间结构,但相对于单一膨润土,TiO₂负载显著提高了材料比表面积;当去离子水:钛酸四丁酯摩尔比=192:1时,在紫外光照射下,复合光催化材料表现出最高的光催化活性,对亚甲基蓝的降解率达到93.8%。